Conventionally, when a substrate to be processed such as, for example, a semiconductor wafer which is processed in a vacuum, an electrostatic chuck device is used to fix the substrate in a vacuum chamber. This kind of electrostatic chuck device has an insulating layer (a dielectric layer) on a susceptor for supporting the substrate. Static electricity occurs by applying voltage between the susceptor and the substrate through the insulating layer, thereby the substrate is attracted by the susceptor.
There are mainly a monopole type and a bipolar type electrostatic chuck mechanism. FIG. 10 shows diagrammatically a configuration of a prior art electrostatic chuck device 1 having the electrostatic chuck mechanism of the bipolar type.
Referring to FIG. 10, an insulating layer 3 on which semiconductor substrate W is placed, is formed on the surface of a susceptor 2. Plural electrostatic chuck electrodes 4A, 4A, 4B and 4B are placed in the inside of the susceptor 2 and positioned to be facing the back surface of the semiconductor substrate W which is placed on the insulating layer 3.
At first, the semiconductor substrate W is placed on the surface of the susceptor 2. Next, the chuck electrodes 4A are connected to a predetermined positive potential source 5A, and the chuck electrodes 4B are connected to a predetermined negative potential source 5B. As a result, the back surface of the semiconductor substrate W is electrified with the polarity shown in FIG. 10. Static electricity occurs between the substrate W and the chuck electrodes 4A and 4B through the insulating layer 3, whereby the semiconductor substrate W is attracted and held to the surface of the susceptor 2.
When the semiconductor substrate W is detached from the susceptor 2, the chuck electrodes 4A and 4B are connected to the ground potential as shown in FIG. 11, respectively, whereby these chuck electrodes 4A and 4B are diselectrified. Thus, the static electricity between the semiconductor substrate W and the chuck electrodes 4A and 4B disappears. Afterwards, the back surface of the semiconductor substrate W is pushed up by lifter pins (not shown), and the semiconductor substrate W is transported to the next process through a transportation robot (not shown).
The chuck electrodes 4A and 4B are generally made of low resistance material (for example carbon, aluminum, copper). Thus, after having interrupted voltage power supply to these chuck electrodes 4A and 4B, if the chuck electrodes chuck 4A and 4B are connected to ground potential, the diselectrification of the chuck electrodes 4A and 4B is completed instantly. In contrast, because the insulating layer 3 made of high resistance material intervenes between the semiconductor substrate W and the chuck electrodes 4A and 4B, diselectrification of the substrate W cannot be performed positively. Therefore, depending on the resistance value of the insulating layer 3, considerable time is needed for diselectrification of the substrate W.
Thus, after having connected the chuck electrodes 4A and 4B to ground potential, there is the case that the electrostatic attraction exists between the back surface of the semiconductor substrate W and the insulating layer 3. In this case, there is a fear that the substrate W will be damaged by the upthrust of the lifter pins or that a transportation error of the substrate W will occur.
Another method for diselectrification of the substrate is to constitute the lifter pins of metal and to connect them to ground potential. As a result, the substrate is diselectrified by contact with the lifter pins. However, depending on the quantity of the electric charge remaining in the substrate W, there is the case that an arc discharge occurs between the substrate and the lifter pins. In this case, discharge signs are formed on the substrate back surface. Furthermore, there is the possibility that the elements on the substrate are damaged.
As conventional substrate diselectrification methods, there are diselectrification by applying reverse voltage, diselectrification by using plasma and diselectrification by heating up the insulating layer to solve such problems.
Diselectrification by applying reverse voltage is a method which provides a reverse electric potential to the chuck electrodes 4A and 4B, and which dissipates the electric charge from the semiconductor substrate W. The method of diselectrification by using a plasma generates a plasma in a process chamber after having connected the chuck electrodes 4A and 4B to ground potential, and dissipates the substrate W through the plasma, as shown typically in FIG. 12 (see patent document 1). The method of diselectrification by heating up the insulating layer 3 is a method which decreases the specific resistance of the insulating layer 3 by raising its temperature and which promotes diselectrification of the semiconductor substrate W.
Patent Document 1: JP2004-14868